Re: [straw] WGLC for draft-ietf-straw-sip-traceroute-01.txt

[Hadriel Kaplan <[e-mail]>]

On Mar 10, 2014, at 3:33 PM, Dawes, Peter, Vodafone Group <[e-mail]> wrote:

> Hi Hadriel,
> Apologies for not being very clear with my comment about lack of clarity :-)
> 
> The draft describes behaviour for a UAC, B2BUA, and UAS. Is the paragraph below from clause 3.1 an instruction to a B2BUA implementer on how to process Max-Forwards or a warning that some B2BUAs will cause the mechanism to fail?

It's an instruction - it has the word "MUST", and it says right at the end:
  ...This document also
  requires such behavior in order to succeed, therefore a B2BUA
  supporting the traceroute mechanism defined in this document MUST
  also comply with [draft-loop-detection].


> A couple of other small questions, is the first sentence "As currently defined in [RFC3261], the UAS half of a B2BUA does not technically need to inspect the Max-Forwards header field value for received requests - only Proxies do. " needed?

Yes, I think it sets the context for this being a change in behavior.


> Also, regarding complying with [draft-loop-detection] does a B2BUA need to do more than "inspect the value in order to prevent loops, as well as copy and decrement the value as if it were a Proxy"? If so it would be good to say something like ", therefore a B2BUA supporting the traceroute mechanism defined in this document MUST also comply with the Max-Forwards behaviour and all other procedures in [draft-loop-detection]"

Isn't that synonymous with "MUST also comply with [draft-loop-detection]"?

I must be missing something obvious to you in reading that paragraph, because it sounds like you're saying it doesn't say X when it says X to me.
:)

-hadriel


> -----Original Message-----
> From: Hadriel Kaplan [mailto:[e-mail]] 
> Sent: 10 March 2014 17:09
> To: Dawes, Peter, Vodafone Group
> Cc: [e-mail]
> Subject: Re: [straw] WGLC for draft-ietf-straw-sip-traceroute-01.txt
> 
> Hi Peter,
> sorry for the delay in responding to this!
> comments inline...
> 
> On Dec 17, 2013, at 7:04 AM, Dawes, Peter, Vodafone Group <[e-mail]> wrote:
> 
>> I think the draft text in clause 3.1 Processing a Received Max-Forwards Header Field (lines 206 - 208)] "As currently defined in [RFC3261], the UAS half of a B2BUA does not technically need to inspect the Max-Forwards header field value for received requests - only Proxies do." should be clearer in terms of what the implementer actually has to do. 
> 
> It says:
>   As currently defined in [RFC3261], the UAS half of a B2BUA does not
>   technically need to inspect the Max-Forwards header field value for
>   received requests - only Proxies do.  This behavior was updated by
>   [draft-loop-detection], such that a compliant B2BUA needs to both
>   inspect the value in order to prevent loops, as well as copy and
>   decrement the value as if it were a Proxy.  This document also
>   requires such behavior in order to succeed, therefore a B2BUA
>   supporting the traceroute mechanism defined in this document MUST
>   also comply with [draft-loop-detection].
> 
> 
> How is that not clear?
> 
> 
>> You replied that "...I think it is in fact in doubt.  I know of many B2BUAs which do in fact decrement max-forwards. (and I think they're right to)". So what does the implementer do? Be happy that they might not need to change too much? Make sure all of their B2BUAs decrement Max-Forwards whether they will loopback media or not? Be aware that if they don't want their B2BUA to decrement Max-Forwards then they can't use this mechanism? Something else?
> 
> See above.
> 
> -hadriel
>